The object is to study the immunologic responses directed against tumour specific antigens during the development of human bladder cancer. Workers in the syestuffs industry exposed to the carcinogens, alpha and beta naphthylamine before 1952 will be studied at regular intervals over a five year period. It is anticipated that during this period a significant number of new cases should arise in a population of 250-300 men considered to be at "great risk". Lymphocytotoxicity, complement mediated serum cytotoxicity, and blocking factor activity will be examined against a panel of allogeneic bladder cancers on each occasion. The results of these tests will be evaluated along with data obtained by regular examination of urine for red cells and malignant cells and where appropriate more detailed examination of the urinary tract including biopsy. It should be possible to determine the time-relationships of the development of lymphocytotoxicity, serum antibody, blocking factor and overt tumour. It is possible that these studies may provide earlier diagnosis and an index of prognosis in carcinogen-induced bladder cancer.